Cathode structure



y c. A. SEGERSTROM, JR 2, ,039

CATHODE STRUCTURE Filed Jan. 31, 1944 2 Sheets-Sh eet l IN V EN TOR. 64/94 H. SEGE/PSTIPOM, J0.

, A?" Am" y 1947. c. A. SEGERSTROM, JR 2, 1, 39

CATHODE STRUCTURE Filed Jan. 31, 1944' 2 Sheets-Sheet 2 INVENTOR. C346; 14. 5565198777001, JR

Patented 27, W47

CATHODE STRUCTURE Carl A. Segerstrom, 3n, Teaneck, N. 3., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application January 31, 1944, Serial No. 520,383 21 Elaims. (Cl. 250-275) This invention relates to improvements in cathode structures, and more particularly to indirectly heated cathodes adapted for use in electron discharge devices.

An object of the present invention is to provide an indirectly heated cathode structure of improved efliciency.

Another object of this invention is to provide an indirectly heated cathode structure in which the heating element concentrates its heat toward the electron-emitting cathode with a minimum of loss.

Still another object of this invention is the provision of an improved heater structure, especially for cathodes of electron discharge devices.

A further object of this invention is to provide an improved cathode structure in which the electron emitting surface is indirectly heated by direct radiation and concentrated reflected heat from an adjacent heating element.

Other objects will become apparent from the following description taken in connection with the attached drawings showing several illustrative embodiments of the invention, and wherein:

Fig. 1 is a vertical cross-sectional view in partial perspective of a vacuum tube illustrating one form of cathode structure in accordance with the present invention;

Fig. 2 is an enlarged top plan view of the cathode heater structure shown in Fig. 1;

Fig. 3 is a partial enlarged cross-sectional view of a detail of the cathode structure;

Fig. 4 is a top plan view of a modified form of cathode heater structure according to the present invention;

Fig. 5 is a transverse cross-sectional view taken along the line 5-5 of Fig. 4;

Fig. 6 is a top plan view of a still further form of cathode heater structure according to the present invention; and

Fig. '7 is a transverse cross-sectional view taken along the line 'i'| of Fig, 6.

Fig. 1 illustrates a preferred form of cathode structure according to the present invention, illustrated, by way of example, as used in one type of high frequency electron-discharge device which is more fully described and claimed in my copending application, S. N. 517,498, filed January 8, 1944, now Patent No. 2,391,927. This tube may be built up on a, metal base ID in the form of a disk having an opening in its center. A second metal disk l2 also having an opening in its center is spaced from a disk ID by means of a glass annulus I4 sealed to suitable extensions on the two disks. A third disk 16 also having a hole in its center is spaced from and supported by the disk l2 by a second glass annulus i8 sealed to extensions on these two disks in a manner known to the art.

About the central opening in the disk l2 may be placed a grid 20, while over the central opening of the disk i6 is placed a hollow metal cylinder 22 having a closed cylindrical extension 24 passing through the opening, the bottom of this extension being spaced adjacent to the grid 20 and forming the tube anode. The main part of the cylinder 22 is sealed to the outer surface of the disk It and it will be seen that this cylinder, together with the disk I8, the glass portion 18, the width of the disk [2 and the glass portion l4 form part of the vacuum tube envelope.

Below the grid structure 20 is positioned a cathode in accordance with the present invention in the form of a metal disk 26 coated with some suitable emissive material and resting on a ceramic or other insulating plate 28. This plate may have imbedded in it a pair of heater coils 30 and 32, spirally interwound, as more clearly indicated in Fig. 2. A lead 34 may be connected to the outer end of the coil 30. a common lead 38 to the center common point of the two heater wires, and a further lead 42 to the outer end of the heater coil 32. The leads 34 and 38 pass through an insulating support 44 sealed within the central opening of the base disk I0 and serve, at the same time, to support the ceramic plate 28 and its superimposed cathode disk 25 in proper spaced relation with the grid 20. Other wires such as 36 may be used to give additional support but they need not pass through the insulating base 44. As seen in Fig. 3, still another lead wire 40 passing through the insulating base 44 may pass upwardly through the ceramic plate 28 and make contact with the metal disk 26 to afford a D. C. cathode lead. The two outer ends of the heater wires 30 and 32 may be interconnected by any suitable means such as a. transverse lead wire 46, which then effectively connects the two heater filaments in parallel. The metal disk 26 is preferably supported out of contact with the heater wires, as by the annular ring 56 on the upper surface of the ceramic plate, and may be attached to this rim in any suitable manner (not shown).

Depending from the periphery of the metal disk 26, I provide a cylinder 48 of some suitable metal foil which, if the device is to be used with high or ultra high frequencies, may be spaced from a, flanged metal sleeve 50 by a cylinder 52 of mica or other insulating material. The

flanged portion or the sleeve Ill may be welded or otherwise attached to the metal base III. the aforedescribed construction thus forming between the cathode 26 and this metal base a series condenser structure. Means such as a spring ring 54 may be used to press the foil 48 against the insulating sleeve and the attached metal sleeve.

It will be noted that the cathode structure described above is relatively simple of manufacture, compact and is most efllcient. The use of metal foil 48 provides a simple built-in condenser structure, and at the'same time this metal foil will conduct little heat away from the cathode disk 26. The heater structure may be most advantageously utilized if the heater coils 30 and 32, as more clearly shown in Fig. 2, are wound with a closer spacing near the periphery of the cathode disk where heat losses may be greater, than near the center. If the internal condenser structure between the cathode and outer disk in is not desired, the metal foil 48 will be readily galvanically connected thereto, as will be obvious to those skilled in this art.

In Figs. 4 and 5 I have illustrated a modified form of cathode heater structure which is adapted to be used in the cathode structure illustrated in Fig. 1. In this case, a plate I28 of ceramic or other insulating material has, in addition to an integral surrounding raised ring I56, a plurality of integral, radiallyextending ribs l 58 provided with radially spaced, generally arcuate notches I60 which hold and support the heater coils 30, 32 on the surface or the plate. In order to concentrate the heat, the surface of the plate may, inturn, be coated with some suitable heatreflecting material, for example, magnesium oxide. The heat from the heater coils is thus even more concentrated toward'the cathode disk which will be supported upon the upper surface of the surrounding, integral ring I56. Heater leads 34, 38 and 42, will be provided as before,

and a supporting wire 36 together with a lead 40 which may pass through the plate to make contact with the cathode disk itself, as illustrated in Fig. 3, may also be utilized.

The heater structure illustrated in Figs. 6 and 7 is similar to that shown in Figs. 4 and 5 except that in this case the heater coils I0 and 32 are supported above a heat-reflecting surface I62 by a plurality of pigtails 284, each having one end wrapped about or otherwise attached to a point on one of the heater coils, and having its other end passing into, and imbedded in the supporting insulating plate. The cathode disk is supported on the ring 56, as before, while the same lead construction which supports the insulating plate 28 from the insulating base may be utilized.

It will, of course, be obvious that the heater structures, particularly those illustrated in Figs. 4 to 7 inclusive, may be of use other than as heater elements for the cathodes of electron discharge devices, and as far as the instant invention is concerned it is not intended to limit the heater structures shown solely for use in connection with such cathodes. In both modified forms of invention I have utilized the double spiral heater construction with variable spacing, as illustrated in Fig. 1, although it will be clear that a single heater coil with other spacing could be utilized, if desired. Accordingly, while I have described above the principles of my invention in connection with speciiic apparatus, and particular modifications thereof. it is to be clearly understood that this description is made only by way of example, and

not as a limitation on the scope 01' my invention as set forth in the objects and the accompanying claims.

I claim:

l. Cathode structure comprising, an insulating plate having an integral upstanding ring on one surface thereof, heating coils carried by said plate, a metal disk carried on said ring out of contact with said heating coils, an insulating base, and means including lead wires attached to said heating coils and metal disk at one end and passing through said insulating base near their other ends, supporting said insulating plate in spaced relation with said insulating base.

2. The combination according to claim 1, in combination with a cylinder of metal 1011 attached at one end about the periphery of said metal disk, and extending toward said insulating base and surrounding said lead wires.

3. The combination according to claim 1, in which said heating coils are in the form of a pair of interwound spirals connected together at their center, the spacing between adjacent turns of the two coils being closer near the outer portion of the insulating plate than at the inner portion thereof.

4. The combination according to claim 1, in combination with a larger metal disk having an opening in its center surrounding and attached to said insulating base, a cylinder of metal foil attached at one end about the periphery of the first metal disk, and means coupling said metal disk to said foil.

5. The combination according to claim 1, in combination with a. larger metal disk having an opening in its center, surrounding and attached to said insulating base, a cylinder of metal foil attached at one end about the periphery of the first metal disk, and capacitative means coupling said metal foil to the larger metal disk.

6. The combination according to claim 1, in combination with a larger metal disk having an opening in its center surrounding and attached to said insulating base. a cylinder of metal foil attached at one end about the periphery of the first metal disk. a metal cylinder attached at one end to said larger metal disk and extending toward said insulating disk inside of said foil cylinder, an insulating cylinder between said foil cylinder and said metal cylinder, and means holding said foil against said insulating and metal cylinders and forming therewith a condenser between the first metal dlsk and the larger metal disk.

7. Cathode structurecomprising an insulating plate having an integral upstanding ring on one surface thereof, and integral grooved supports below the upper surface of said ring, heating coils carried by said plate in said grooves, a metal disk carried on said ring out of contact with said heating coils, an insulating base, and means including lead wires attached to said heating coils and metal disk at one end and passing through said insulating base near their other ends, supporting said insulating plate in spaced relation with said insulating base.

8. The combination according to claim 7, in combination with a cylinder of metal foil attached at one end about the periphery of said metal disk. and extending toward said insulating base and surrounding said lead wires.

9. The combination according to claim 7, in which saidheatlng coils are in the form of a pair of interwound spirals connected together at their center, the spacing between adjacent turns of heating coil on said plate above said reflecting means but below the upper surface of said ring, a metal disk carried on said ring out of contact with said heating coil, an insulating base, and means including lead wires attached to said heating coil and metal disk at one end and passing through said insulating base near their other ends, supporting said insulating plate in spaced relation-with said insulating base.

11. The combination according to claim 10, in combination with a cylinder of metal foil attached at one end about the periphery of said metal disk, and extending toward said insulating base and surrounding said lead wires.

12. The combination according to claim 10, in which said heating coil is in the form of a pair of interwound spirals connected together at their center, the spacing between adjacent turns of the two spirals being closer near the outer portion of the insulating plate than at the inner portion thereof.

13. Cathode structure comprising an insulating plate having an integral upstanding ring on one surface thereof, and a plurality of integral, angularly-spaced ribs extending inwardly from said ring toward the center of said plate, each of said ribs being provided with a plurality of radially spaced, generally arcuategrooves. a spiral heating coil carried by said groove above the surface of the plate, heat-reflecting means on said surface, a metal disk carried on said ring, an insulating base, and means including lead wires attached to said heating coil and metal disk at one end and passing through said insulating base near their other ends, supporting said insulating plate in spaced relation with said insulating base.

14. The combination according to claim 18, in combination with a cylinder of metal foil attached at one end about the periphery of said metal disk, and extending toward said insulat- 1 ing base and surrounding said lead wires.

15. The combination according to claim 13. in which said heating coil is in the form of a pair of interwound spirals connected together at their center. the spacing between adjacent turns of the two spirals being closer near the outer portion of the insulating plate than at the inner portion thereof.

16. Cathode structure comprising an insulating plate having an integral upstanding ring on one surface thereof, heat-reflecting means covering said surface, a heating coil, means supporting said heating coil above said reflecting surface and below the upper surface of said ring, said means including a plurality of spaced, fine wire pigtails, each having one end wrapped about spaced points on said heating coil and its other end imbedded in said insulating plate, a metal disk carried on said ring out of contact with said heating coil, an insulating base, and means including lead Wires attached to said heating coil and metal disk on one end and passing through said insulating base near their other ends, supporting said insulating plate in spaced relation with said insulating base.

17. The combination according to claim 16, in combination with a'cylinder of metal foil attached at one end about the periphery of said metal disk, and extending toward said insulating base and surrounding said lead wires.

18. The combination according to claim 16, in which said heating coil is in the form of a pair of interwound spirals connected together at their center, the spacing between adjacent turns of the two spirals being closer near the outer portion of the insulating plate than at the inner portion thereof.

19. Cathode structure comprising a, flat wound wire heating element and a metallic plate coated with emitting materials in close spaced parallel relation with said element, the wire of said element towards the perimeter thereof being spaced more closely together than towards the center thereof.

20. In an electron discharge device, a unitary condenser and cathode assembly, the cathode comprising a metal plate, said plate being electron emissive on one side, and a heating element adjacent the other side of said plate; the condenser comprising two coaxial insulatingly spaced metal cylinders capacitively coupled, the rim of one cylinder being electrically connected along the periphery of said plate. and an electrical connection to the rim of the other cylinder.

21. In an electron discharge device, a cathode assembly comprising a sheet metal member electron emissive on one side, a heating element ad- 'jacent the other side of the member, two coaxial metal cylinders and a cylinder of insulating material, the cylinder of insulating material being telescoped between the two metal cylinders, the rim of one of said metal cylindersbeing directly connected to the edge of said member.

CARL A. SEGERSTROM, Jn.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES .PA'I'ENTS Number Name Date 2,300,891 Hanks Nov. 3, 1942 1,539,497 Longoria May 26, 1925 1,102,249 Denhard July 7,1914 2,051,637 Goldbert et al Aug. 18, 1936 2,357,905 Olving Sept. 12, 1944 2,367,332 Bondley Jan. 16, 1945 1,866,195 Creuze July 5, 1932 FOREIGN PATENTS Number Ooimtry Date 700,923 France Aug. 21, 1930 

